1. Field of the Invention
This invention relates to a data-base management software system, and in particular to an improved real-time distributed data-base management system configured for high-speed operation.
2. Prior Art
A data-base management system (DBMS) is a generalized software system designed to provide facilities for data base organization, access, and control. A data base is a collection of logically organized information intended for access by multiple users. The data base constitutes the collective requirements of all users. However, any individual user would typically require access to only a portion of the entire data base.
In a distributed data processing system having multiple computer processors, a general problem arises as to the most efficient organization of the data base and optimum procedures for accessing that data base while minimizing required system resources. The problem becomes particularly acute in real-time computer operating environments, such as are used to control manufacturing processes. In such an environment, various of the processors require access to data that is constantly changing, such as temperature, pressure, flow rate, and other manufacturing process parameters that are input into the computer processing system for evaluation and control of the manufacturing process.
FIG. 1 shows a block diagram of a typical multiple processor computer architecture used for real-time manufacturing process control. Each processor is coupled to a communications bus, which may be one of several communications bus types. Typically, in a real-time operating system, each local processor 2a . . . 2n receives data from or sends data to a number of subprocessors 3. The subprocessors 3 are coupled to sensors and/or actuators 4, for interaction with the manufacturing process. Often one processor will need data collected by another processor to update calculations used in the manufacturing process control. For example, one local processor may obtain temperature data on a portion of a manufacturing process. This temperature data must be used by a second processor in order to limit the rate of flow of material in another portion of the manufacturing process. However, it is rare that any one processor needs access to all of the data being collected by all of the processors in the system. Therefore, it would be wasteful of processing system resources to store duplicate copies of the complete data base in each local processor. Further, it would be wasteful of system communication resources to update each such data base in each processor whenever the data changes. Thus, it is advantageous to devise a data base architecture that provides access by one processing unit to data in another processing unit upon demand.
Some prior art systems have utilized a centralized data base in a main processor, which each local processor accesses as necessary to ascertain the current value of particular variables. However, this architecture is not very reliable, since a failure in the main processor may completely disrupt operation of the processing system as a whole. Examples of such prior art systems may be found in "Distributed Micro/Minicomputer Systems" by Cay Weitzman (Prentice-Hall, Inc. copyright 1980).
It is advantageous in a real-time computer processing system to permit each local processor to locally store and directly address data that is necessary in the operation of that processor. Such direct addressing permits improved performance by permitting the processor to fetch data from its local memory without having to calculate or otherwise locate the address of that information. Such local storage of necessary information is also advantageous in providing higher reliability for the system as a whole, since, by locally storing data acquired from another processor, no one processor is dependent upon the accessibility and reliability of a centralized data base. It is also advantageous to provide a real-time data base management system that permits automatic update of data used in a local processor but originally obtained from another processor.
Therefore, it is an object of the present invention to provide an improved real-time data base management system which minimizes the memory requirements of each local processor, provides high reliability by locally storing data used in each processor, and minimizes the amount of processing time incurred in transferring data from one processor to another processor.